The invention relates to a method for operating an internal combustion engine, in particular of a motor vehicle, in which fuel is delivered by a fuel pump into a pressure reservoir, in which the delivery quantity of the fuel pump can be changed, and in which the fuel quantity supplied to the pressure reservoir is adjusted to a required fuel quantity by influencing the delivery quantity of the fuel pump. The invention also relates to an internal combustion engine, in particular for a motor vehicle, having a fuel pump with which fuel can be delivered into a pressure reservoir and having a control device that is connected to the fuel pump, wherein the delivery quantity of the fuel pump can be changed and wherein the fuel quantity supplied to the pressure reservoir can be adjusted to a required fuel quantity by influencing the delivery quantity of the fuel pump.
This kind of method and internal combustion engine are generally known. The fuel is fed into a pressure reservoir of the internal combustion engine by a first fuel pump, which is usually driven in an electromotive fashion, and by a second high-pressure pump, which is usually mechanical. The fuel quantity delivered can be changed, for example, by means of a corresponding influence on the electromotively driven first fuel pump. In this manner, the respectively required fuel quantity is supplied to the pressure reservoir. The injection valves are connected to the pressure reservoir, with the aid of which the fuel is injected into the individual cylinders of the internal combustion engine. The required fuel quantity supplied to the pressure reservoir thereby corresponds largely to the fuel quantity injected into the cylinders of the engine by the injection valves.
The object of the invention is to develop a method for operating an internal combustion engine as well as to produce an internal combustion engine in which the required fuel quantity is supplied to the pressure reservoir in the simplest possible manner.
This object is attained according to the invention with a method of the type mentioned at the beginning by virtue of the fact that the fuel quantity of the fuel pump is controlled via a program map as a function of a number of input variables. The object is also attained according to the invention with an internal combustion engine of the type mentioned at the beginning by virtue of the fact that the control device can control the delivery quantity of the fuel pump via a program map as a function of a number of input variables.
The delivery quantity of the fuel pump and thereby the fuel quantity supplied to the pressure reservoir is consequently controlled via the program map. This kind of map-dependent control represents a simple, but extremely effective manner of influencing the delivery quantity of the fuel pump and thereby the adjustment to the required fuel quantity. As a result, no significant expense is required in order to control the delivery quantity of the fuel pump.
It is particularly advantageous if the delivery quantity of the fuel pump is controlled via the program map as a function of the fuel quantity to be injected and/or the speed of the engine and/or the temperature of the intake air and/or the battery voltage. With the aid of these input variables, it is possible by simple means to generate a program map and to control the delivery quantity of the fuel pump via this program map.
In a preferred embodiment of the invention, the program map is equalized during a startup of the engine, particularly at the beginning of the startup.
In this manner, it is possible to equalize tolerances of different fuel pumps as well as age-related changes. The tolerances and changes are therefore taken into account and can be compensated for. The tolerances and also the changes consequently have no negative influence on the map-dependent control of the delivery quantity of the fuel pump.
It is particularly advantageous if the program map is equalized with each startup of the engine. In this instance, even extremely small changes in the fuel pump can be detected with each startup of the engine and can therefore be immediately taken into account. This produces a particularly precise and reliable control of the delivery quantity of the fuel pump.
In a preferred modification of the invention, the program map is equalized when the ignition contact of the engine is switched on, and/or the program map is equalized when the speed of the engine is lower than a predetermined threshold value. With these alternative or mutually supplementary measures, it is possible to detect a startup of the engine in a simple manner. Thus, it is possible on the one hand for the program map to be equalized when the ignition of the engine is switched on by the driver. It is likewise possible for the program map to be equalized when the speed of the engine is below the predetermined threshold value. These two measures can be used individually or in combination.
In a preferred embodiment of the invention, the actual value of the pressure in the pressure reservoir is measured, a reference value of the pressure in the pressure reservoir is determined as a function of the required fuel quantity, and the actual value and reference value are compared to each other and the program map is equalized a function of this comparison.
The equalization of the program map consequently occurs in a pressure-dependent fashion. The reference value and the actual value of the pressure in the pressure reservoir are compared to each other for this purpose. If there is a difference between them, then this means that the reference value generated by means of the map-dependent control does not result in an identical actual value. As a result, the program map is influenced and changed in such a way or until the actual value corresponds to the predetermined reference value. If so desired or if necessary, this equalization of the program map can be carried out not only at the beginning but also possibly during the actual startup of the engine.
In an advantageous improvement of the invention, the pressure in the pressure reservoir can be changed by means of a valve associated with the pressure reservoir and the valve is open during the equalization of the program map. This changes a pressure increase in the pressure reservoir during the equalization of the program map. It is consequently assured that during the equalization, only the map-dependent control acting via the fuel pump determines the pressure in the pressure reservoir. This simple measure achieves the fact that the comparison of the actual value to the reference value of the pressure in pressure reservoir is sufficient for the equalization of the program map.
Other features, potential applications, and advantages of the invention ensue from the subsequent description of exemplary embodiments of the invention which are shown in the drawings. All of the features described or depicted, whether by themselves or in arbitrary combinations, constitute the subject of the invention, independent of their combination in the claims or their dependencies and independent of their formulation or depiction in the description or in the drawings.